Peptidoglycan synthesis drives an FtsZ-treadmilling-independent step of cytokinesis

Peptidoglycan is the main component of the bacterial wall and protects cells from the mechanical stress that results from high intracellular turgor. Peptidoglycan biosynthesis is very similar in all bacteria; bacterial shapes are therefore mainly determined by the spatial and temporal regulation of peptidoglycan synthesis rather than by the chemical composition of peptidoglycan. The form of rod-shaped bacteria, such as Bacillus subtilis or Escherichia coli, is generated by the action of two peptidoglycan synthesis machineries that act at the septum and at the lateral wall in processes coordinated by the cytoskeletal proteins FtsZ and MreB, respectively^1,2. The tubulin homologue FtsZ is the first protein recruited to the division site, where it assembles in filaments—forming the Z ring—that undergo treadmilling and recruit later divisome proteins^3,4. The rate of treadmilling in B. subtilis controls the rates of both peptidoglycan synthesis and cell division³. The actin homologue MreB forms discrete patches that move circumferentially around the cell in tracks perpendicular to the long axis of the cell, and organize the insertion of new cell wall during elongation^5,6. Cocci such as Staphylococcus aureus possess only one type of peptidoglycan synthesis machinery^7,8, which is diverted from the cell periphery to the septum in preparation for division⁹. The molecular cue that coordinates this transition has remained elusive. Here we investigate the localization of S. aureus peptidoglycan biosynthesis proteins and show that the recruitment of the putative lipid II flippase MurJ to the septum, by the DivIB–DivIC–FtsL complex, drives peptidoglycan incorporation to the midcell. MurJ recruitment corresponds to a turning point in cytokinesis, which is slow and dependent on FtsZ treadmilling before MurJ arrival but becomes faster and independent of FtsZ treadmilling after peptidoglycan synthesis activity is directed to the septum, where it provides additional force for cell envelope constriction.

 

a, Schematic of the peptidoglycan synthesis pathway in S. aureus. UDP, uridine diphosphate. b, Structured illumination microscopy (SIM) images of S. aureus cells expressing fluorescent derivatives of PG synthesis proteins. Scale bars, 0.5 μm. Images are representative of three biological replicates. c, Ratios between fluorescence signal at the septum and the peripheral membrane, measured in cells with a complete septum (phase 3). Blue, membrane proteins with fluorescence ratio of approximately 2, similar to Nile Red staining of COL membrane (expected as the septum contains two membranes versus one in the cell periphery). Green, septal enriched proteins with 2.5 < fluorescence ratio < 3.5. Red, septal proteins with fluorescence ratio > 4. Data are represented as column graphs in which the height of the column is the mean and whiskers are s.d. From left to right, n = 439, 533, 516, 513, 512, 622, 503, 517, 503, 689, 1,321, 488 and 516 cells. AU, arbitrary unit. d, Schematic of the S. aureuscell cycle. Phase 1 cells have not initiated septum synthesis, phase 2 cells are undergoing septum synthesis and phase 3 cells have a complete septum undergoing maturation in preparation for splitting.

Enlace al trabajo

Construcción de cepas de Escherichia coli a partir de minicélulas por transferencia lateral de genes

Recently, artificial life is created with artificial materials and methods. Life can be born, when genomic DNA molecule integrated in liposomes containing biochemical reactions for biogenic needs. However, it is not yet known whether the integration of these parts will be able to occur in nature, and constitute a living system. I planned to regenerate bacteria from biologically active liposomes by inserting genomic DNA using all natural materials and methods. The mini-cells of Escherichia coli, containing plasmids and activated SOS proteins, act as protocells. Four new E. coli strains were regenerated from mini-cells by inserting the genomes with the conjugation system between F^- and Hfr strains. Four regenerated cells showed the same genetic markers as two genome donors. The pulse field gel electrophoresis of their genomes showed admixing of those of both two donors. In addition, the genome of 4 regenerated cells had chimera genome of two donors. Our results represent synthesis of life can occur in nature without artificial arrangement.

IMPORTANCE What is the difference between inanimate objects and organisms? Organisms have genomic DNA by all means. When organisms lose their genome, they cannot neither grow nor reproduce. As the result, organisms turn into inanimate objects without their genome. In this manuscript, I regenerated microbes from the cell corpse that lost its genome by inserting another genome. All steps of regeneration applied natural behavior of microbes. The same regeneration of microbes would happen in nature. The primitive lives have plasticity, which accelerates evolution and provides various kinds of lives in the world.

Enlace al trabajo

Sistemas de inyección contráctil de bacteriófagos

Bacteria and bacteriophages utilize a  rigid  tube-contractile  sheath  mechanism  for delivering proteins and DNA across the cell envelope. Here we describe conserved features of these contractile assemblies and propose their evolutionary pathway. The complexity of today’s systems is a result of gene duplication and subsequent specialization of function.

Contractile    tail    bacteriophages, or    myobacteriophages, use    a    sophisticated biomolecular structure to inject their genome into the bacterial host cell.  This structure consists of a contractile sheath enveloping a rigid tube that is sharpened by a spike-shaped protein complex at its tip. The spike complex forms the centerpiece of a baseplate complex that terminates the sheath and the tube.  The baseplate anchors the tail to the target  cell membrane  with  the  help  of  fibrous  proteins  emanating  from  it  and  triggers  contraction  of  the sheath. The contracting sheath drives the tube with its spiky tip through the target cell membrane.  Subsequently, the bacteriophage genome  is  injected  through  the tube.  The structural transformation of  the  bacteriophage  T4  baseplate  upon  binding  to  the  host  cell  has  been  recently  described  in  near-atomic  detail. 

Enlace al trabajo